Video content is generally associated with an aspect ratio. This aspect ratio is the intended ratio between the width and the height of a display area in which the video content will be displayed. Aspect ratios are given in the form width:height. For example, until recently, televisions have generally had a display area with an aspect ratio of 4:3, that is to say, the height of the screen is 75% of the width of the screen. This is known as a “full screen” or “standard definition” aspect ratio. Widescreen displays are also available. The width of a widescreen television with a display area of a certain height is greater than the width of a standard display area for that certain height. Thus, a widescreen aspect ratio will be higher than a standard display area aspect ratio. A typical widescreen aspect ratio is 16:9. While widescreen displays are becoming more prevalent, much existing content (for example, broadcast television) is in a standard aspect ratio of 4:3 or another aspect ratio.
A problem occurs when content of one aspect ratio is to be displayed in a display area of a different aspect ratio. In order to display content of a certain aspect ratio on a display with a higher aspect ratio (e.g., to display content of a standard aspect ratio on a widescreen display), a technique known as pillarboxing is used. In the pillarboxing technique, the content is displayed on the widescreen display using the entire height of the widescreen display, but not the entire width of the display. FIG. 1 is a block diagram of the prior art pillarboxing technique for displaying video content of one aspect ratio on a display with a second, higher aspect ratio. As shown in FIG. 1, the widescreen display 10 contains standard aspect ratio display area 20. The height of the standard aspect ratio display area is the same as the height of widescreen display 10. However, standard aspect ratio display area 20 is narrower than the widescreen display 10. The remaining area on widescreen display 10 are pillarbox areas 30. These areas do not display the standard aspect content. Often these pillarbox areas are blacked out or otherwise filled by content which will not distract a viewer from the content in the standard aspect display area 20.
The result of pillarboxing is shown in FIG. 2. FIG. 1 is a diagram of the prior art pillarboxing technique in use. As shown in FIG. 2, pillarboxing areas 30 are the blacked out areas on either side of the standard aspect display area 20. The standard aspect display area 20 is displaying the standard aspect content. This prior art pillarboxing technique has at least two major drawbacks: the first is that a user of a widescreen display 10 may be disappointed that only the standard aspect ratio display area 20 of widescreen display 10 is in use. The second is that some displays, for example some plasma displays, may get a “burn-in” effect from displaying the pillarboxes 30 for extended times. This burn-in may cause a loss in display performance, for example, after extended use of a display using the pillarbox technique, a “shadow” of the pillarboxes may be visible to the user when the entire widescreen display 10 is being used.
Another prior art technique for displaying video content of one aspect ratio on a display with a different aspect ratio is to stretch the content uniformly over the display. The image is displayed as intended in one dimension (top to bottom) but in the other dimension (side to side) the image is uniformly stretched. In order to display an image, given an aspect ratio (the original aspect ratio of the video content) and a height (the height of the display), an intended width can be calculated. However, because the aspect ratio of the display is different than that of the video content, this intended width would not fill the display. The prior art technique stretches the video content to a width which will fill the entire display. This may be accomplished, for example, using a stretching method in a graphics interface which interfaces with graphics hardware. The stretching may also be accomplished by using a stretching capability in the graphics processing unit itself. Such stretching simply allows for a uniform linear stretch of a rectangular area to fill a greater area. FIG. 3 is a diagram of an example of the use of the prior art uniform stretch-to-fit technique on the image from FIG. 2. In FIG. 3, the entire widescreen display 10 is used to display an image. This uniform stretch technique may also allow a uniform linear shrink to be used if the aspect ratio of the display is smaller than the aspect ratio of the source video content.
Thus, uniform stretching can allow the use of the a display of a different aspect ratio than the source image. However, since the image was originally intended for display on a screen with a lower aspect ratio than the widescreen display 10, the image appears distorted. The image may appear “fat” (where the aspect ratio of the display is higher than that of the source content) or squeezed (where the aspect ratio of the display is lower than that of the source content.) This distortion is one disadvantage of this prior art technique.
In view of the foregoing, there is a need for a system and method that overcomes the drawbacks of the prior art.